Poly(ADP-ribose) polymerases (PARPs) are members of a family of seventeen enzymes that regulate fundamental cellular processes including gene expression, protein degradation, and multiple cellular stress responses (Vyas S, et al. Nat Rev Cancer. 2014 Jun. 5; 14(7):502-509). The ability of cancer cells to survive under stress is a fundamental cancer mechanism and an emerging approach for novel therapeutics. One member of the PARP family, PARP1, has already been shown to be an effective cancer target in connection to cellular stress induced by DNA damage, either induced by genetic mutation or with cytotoxic chemotherapy, with three approved drugs in the clinic and several others in late stage development (Ohmoto A, et al. OncoTargets and Therapy. 2017; Volume 10:5195).
The seventeen members of the PARP family were identified in the human genome based on the homology within their catalytic domains (Vyas S, et al. Nat Commun. 2013 Aug. 7; 4:2240). However, their catalytic activities fall into 3 different categories. The majority of PARP family members catalyze the transfer of mono-ADP-ribose units onto their substrates (monoPARPs), while others (PARP1, PARP2, TNKS, TNKS2) catalyze the transfer of poly-ADP-ribose units onto substrates (polyPARPs). Finally, PARP13 is thus far the only PARP for which catalytic activity could not be demonstrated either in vitro or in vivo. PARP14 is a cytosolic as well as nuclear monoPARP. It was originally identified as BAL2 (B Aggressive Lymphoma 2), a gene associated with inferior outcome of diffuse large B cell lymphoma (DLBCL), together with two other monoPARPs (PARP9 or BAL1 and PARP15 or BAL3) (Aguiar R C, et al. Blood. 2000 Dec. 9; 96(13):4328-4334 and Juszczynski P, et al. Mol Cell Biol. 2006 Jul. 1; 26(14):5348-5359). PARP14, PARP9 and PARP15 are also referred to as macro-PARPs due to the presence of macro-domains in their N-terminus. The genes for the three macroPARPs are located in the same genomic locus suggesting co-regulation. Indeed, the gene expression of PARP14 and PARP9 is highly correlated across normal tissues and cancer types. PARP14 is overexpressed in tumors compared to normal tissues, including established cancer cell lines in comparison to their normal counterparts. Literature examples of cancers with high PARP14 expression are DLBCL (Aguiar R C T, et al. J Biol Chem. 2005 Aug. 1; 280(40):33756-33765), multiple myeloma (MM) (Barbarulo A, et al. Oncogene. 2012 Oct. 8; 32(36):4231-4242) and hepatocellular carcinoma (HCC) (lansante V, et al. Nat Commun. 2015 Aug. 10; 6:7882). In MM and HCC cell lines RNA interference (RNAi) mediated PARP14 knockdown inhibits cell proliferation and survival. Other studies show that the enzymatic activity of PARP14 is required for survival of prostate cancer cell lines in vitro (Bachmann S B, et al. Mol Cancer. 2014 May 27; 13:125).
PARP14 has been identified as a downstream regulator of IFN-γ and IL-4 signaling, influencing transcription downstream of STAT1 (in the case of IFN-γ) (Iwata H, et al. Nat Commun. 2016 Oct. 31; 7:12849) or STAT6 (in the case of IL-4) (Goenka S, et al. Proc Natl Acad Sci USA. 2006 Mar. 6; 103(11):4210-4215; Goenka S, et al. J Biol Chem. 2007 May 3; 282(26):18732-18739; and Mehrotra P, et al. J Biol Chem. 2010 Nov. 16; 286(3):1767-1776). Parp14−/− knockout (KO) mice have reduced marginal zone B cells, and the ability of IL-4 to confer B cell survival in vitro was reduced as well in the Parp14 KO setting (Cho S H, et al. Blood. 2009 Jan. 15; 113(11):2416-2425). This decreased survival signaling was linked mechanistically to decreased abilities of Parp14 KO B cells to sustain metabolic fitness and to increased Mcl-1 expression. Parp14 KO can extend survival in the Eμ-Myc lymphoma model, suggesting a role of PARP14 in Myc-driven lymphomagenesis (Cho S H, et al. Proc Natl Acad Sci USA. 2011 Sep. 12; 108(38):15972-15977). Gene expression data point towards roles of PARP14 in human B cell lymphoma as well. The BAL proteins, including PARP14, are highly expressed in host response (HR) DLBCLs, a genomically defined B cell lymphoma subtype characterized with a brisk inflammatory infiltrate of T and dendritic cells and presence of an IFN-γ gene signature (Molecular profiling of diffuse large B-cell lymphoma identifies robust subtypes including one characterized by host inflammatory response. Monti S, et al. Blood. 2005; 105(5):1851). Indeed, PARP14 is believed to be an interferon stimulated gene with its mRNA increased by stimulation of various cell systems with all types of interferon (I, II and III; www.interferome.org).
Due to its role downstream of IL-4 and IFN-γ signaling pathways PARP14 has been implicated in T helper cell and macrophage differentiation. Genetic PARP14 inactivation in macrophages skews to a pro-inflammatory M1 phenotype associated with antitumor immunity while reducing a pro-tumor M2 phenotype. M1 gene expression, downstream of IFN-γ, was found to be increased while M2 gene expression, downstream of IL-4, was decreased with PARP14 knockout or knockdown in human and mouse macrophage models. Similarly, genetic PARP14 knockout has been shown to reduce a Th2 T helper cell phenotype in the setting of skin and airway inflammation, again pertaining to the regulatory role of PARP14 in IL-4 signal transduction (Mehrotra P, et al. J Allergy Clin Immunol. 2012 Jul. 25; 131(2):521 and Krishnamurthy P, et al. Immunology. 2017 Jul. 27; 152(3):451-461).
PARP14 was shown to regulate the transcription of STAT6 (activator of transcription 6) and promotes TH2 responses in T cells and B cells, which are known to promote allergic airway disease (asthmatic condition). Genetic depletion of PARP14 and its enzymatic activity in a model of allergic airway disease led to reduced lung inflammation and IgE levels, which are key readouts of the asthmatic process in this model. In addition, the enzymatic activity of PARP14 promoted a TH2 phenotype differentiation in a STAT6 dependent manner. (Mehrotra P, et al. J Allergy Clin Immunol. 2012 Jul. 25; 131(2):521) Therefore, inhibition of the PARP14 catalytic activity may be a potential novel therapy for allergic airway disease.
There is an ongoing need for new medications that can treat diseases such as certain cancers and inflammatory conditions characterized by abnormal expression or activity of PARP14. The compounds, compositions, and methods described herein help meet these and other needs.